A Polymer Monolith Incorporating Stellate Mesoporous Silica

Microchimica Acta (2018) 185: 444 https://doi.org/10.1007/s00604-018-2964-6

ORIGINAL PAPER

A polymer monolith incorporating stellate mesoporous silica nanospheres for use in capillary electrochromatography and solid phase microextraction of polycyclic aromatic hydrocarbons and organic small molecules

Xiu-Jie Zhou1 & Li-Shun Zhang 1 & Wen-Fang Song1 & Yan-Ping Huang1 & Zhao-Sheng Liu1

Received: 15 May 2018 /Accepted: 16 August 2018 /Published online: 3 September 2018 # Springer-Verlag GmbH Austria, part of Springer Nature 2018

Abstract An inorganic-organic hybrid monolith incorporated with stellated mesoporous silica nanoparticles (SMSNs) was prepared. Using binary solvents, deep eutectic solvents and room temperature ionic liquids, an SMSN-incorporated poly(butyl methacrylate-co- ethylene glycol dimethacrylate) monolith demonstrated uniform structure with good column permeability. A systematic investigation of preparation parameter was performed, including SMSN content, crosslinking monomer content, and the component of binary solvent. The optimized monoliths were characterized by field emission scanning electron microscopy, transmission electron microscopy, area scanning energy dispersive spectrometry, and nitrogen adsorption. Column performance was tested by separating four groups of analytes (alkylbenzenes, anilines, naphthalenes and phenols) by capillary electrochromatography (CEC). Baseline separation of all analytes was obtained with column efficiencies of up to 266,000 plates m−1. The performance of the resulting monolith was further investigated in detail by separating mixtures of polycyclic aromatic hydrocarbons (PAHs), nonsteroidal antiinflammatory drugs (NSAIDs), and hydroxybenzoic acid isomers. Compared with the corresponding SMSN- free monolith, the CEC performance was improved by about six times. Successful extraction of PAHs and quinolones (QNs) were also performed using this capillary. Improved extraction efficiency (20.2%) for complex samples, lake water, was also found when the material was applied to solid phase microextraction of fluoranthene.

Keywords Capillary monoliths . Room temperature ionic liquids . Deep eutectic solvents . Small organic molecules . Environmental pollutant . Antibiotics . Lake water . Column efficiency . Quinolones . Hydroxybenzoic acid

Introduction reported have demonstrated several attractive merits, such as fast mass transfer, ease of preparation, controllable porosity Polymer-based monolithic columns are versatile materials ex- and excellent permeability [1, 2]. They have been applied for tensively applied in analytical science. The polymer monoliths pharmaceuticals, biomedicine, food control, environmental analysis and agricultural research [3–5]. Nevertheless, prepar- Xiu-Jie Zhou and Li-Shun Zhang contributed equally to this work. ing polymer monoliths with column efficiency comparable with particulate and monolithic silica-based stationary phases Electronic supplementary material The online version of this article (https://doi.org/10.1007/s00604-018-2964-6) contains supplementary has been proven to be difficult since the original monolithic material, which is available to authorized users. polymer has smaller surface areas due to absence of nanopores and mesopores in polymer matrix [2, 3]. * Yan-Ping Huang For overcoming the disadvantages above, plentiful strate- [email protected] gies were studied, including innovative polymerization condi- * Zhao-Sheng Liu tions, nanomaterial incorporation and hypercrosslinking [email protected] [6–8]. Among the above strategies, multifunctional polymer nanocomposites are popular and extensive fields. The merit of 1 Tianjin Key Laboratory on Technologies Enabling Development of such nano-entities separation media is that the stationary Clinical Therapeutics and Diagnostics (Theranostics), School of Pharmacy, Tianjin Medical University, Tianjin 300070, China phases can be formed with more surfaces area [9]. To date, 444 Page 2 of 10 Microchim Acta (2018) 185: 444 plenty of nano materials, including carbon nanotubes (CNT) 3-(trimethoxysilyl) propyl methacrylate (γ-MPS) to yield the [10], graphene oxide (GO) [11], metal-organic frameworks Bhybrid^ methacryloyl silica nanoparticle monomer. The op- [12], mesoporous molecular sieve [13] and hydroxyapatite timized SMSN incorporated monolithic column was charac- [14] have been incorporated into neat monolithic polymer. terized with area scanning energy dispersive spectrometry,

Surface chemistry with tailored selectivity can be observed field emission scanning electron microscopy, N2 adsorption on the hybrid monoliths due to the unique surface properties experiment and transmission electron microscopy. of nanoparticles. Evaluation of chromatographic performance, including sepa- Silica nanoparticles have attracted wide attention for their ration ability and column efficiency, was conducted in capil- remarkable properties, including great surface area, high or- lary electrochromatography (CEC) mode. In addition, the ganic solvent resistance, good biocompatibility and easily SMSN incorporated monolith was also used as solid phase postmodification with distinct functional groups [15]. microextraction (SPME) for extraction of complex samples. Typically, silica nanoparticles can be functionalized at the first step with the following step of dynamical coating on the inner of the capillary to alter EOF or adding to background electro- Experimental materials and methods lyte solution [16]. For example, fumed silica nanoparticles (FSNPs) having specific surface of ~ 200 m2/g and an average Chemical reagents and materials primary particle size of ~ 12 nm were used to prepare polymethacrylate-based monolithic column [17, 18]. With Chemicals and reagents employed were at least analytical successful separation of small solutes and proteins, incorpo- grade in this work. Anthracene, acenaphthylene, fluorine, rating distinct properties of silica nanoparticles into monolith- fluoranthene, pyrene, naphthalene, benzo (b) fluoranthene, ic column is considered as another valid method to improve benzo (a) anthracene, 1-methylnaphthalene, 1- chromatographic performance successfully for hydrophilic in- choronaphthalene, 1-bromonaphthalene, 1-naphthol, resorcin- teraction high performance liquid chromatography and ol, m-cresol, 2,6-dichlorphenol, toluene, ethylbenzene, reversed-phase chromatography. propylbenzene, butylbenzene, choline chloride (ChCl) were Stellated mesoporous silica nanoparticles (SMSN) are nov- all obtained from Aladdin (Shanghai, China, www.aladdin-e. el nanoparticles with a special structure of stellated emboss- com). 2,5-Dihydroxyacetophenone (98%), butyl methacrylate ment around silica nanoparticles, thus higher specific surface (BMA) and azobisisobutyronitrile (AIBN) were purchased area (> 500 m2/g) and average diameter (80 nm) than FSNPs. from J&K Scientific Ltd. (Beijing, China, www.jkchemical. Traditionally, the smaller the size of the nanoparticles, the com). All the RTILs (98%) were purchased form Chengjie greater the specific surface area of the resultant materials. Chemical Co. Ltd. (Shanghai, China, www.ionicliquid.com. Thus, the nature of SMSN opposed to conventional nanopar- cn). Acetonitrile (ACN, HPLC grade), 3-(trimethoxysilyl) ticles. It is expected that incorporation of SMSN into mono- propyl methacrylate (γ-MPS, 98%), 2-acrylamido-2-methyl- lithic matrix will improve the specific surface area and avoid propanesulfonic acid (AMPS, 98%), butyrophenone (99%) low column permeability. In view of the facts above, it is and ethylene glycol dimethacrylate (EDMA, 98%) were pur- intriguing for us to investigate whether extraordinary nature chased form Sigma-Aldrich (St. Louis, MO, USA, www. of SMSN can be utilized to increase column efficiency of sigmaaldrich.com). Other reagents were supplied by Tianjin monolith. However, the challenge of preparing SMSN-based Chemical Reagent Co. Ltd. (Tianjin, China, www.630451. hybrid monolithic matrix with homogeneous structure is the atobo.com.cn). Real water sample was collected by Jingyi difficulty in suspending SMSN in conventional porogen due Lake in Tianjin Medical University. Stellate mesoporous to the larger size [15]. silica nanosphere (SMSN) was purchased from XFNANO A binary porogen system, room temperature ionic liquids Materials Tech. Co., Ltd. (Nanjing, China, www.xfnano. (RTILs) and deep eutectic solvents (DESs), has been found to com). Fused-silica capillary (375 μm OD, 100 μmID; afford hybrid monolithic matrix with homogeneous structure 375 μm OD, 250 μm ID) was purchased from Xinnuo Optic and good permeability [10, 13]. When RTILs were used alone Fiber Plant (Hebei, China, www.11467.com/handan/co/ as porogenic solvents in preparing multifunctional nanocom- 68426.htm). posites, nanoparticles suspension can be sustained for fairly long time in prepolymerization mixture [19]. It has also been found that DESs can provide good solubility for polymeriza- Silylation modification of pristine SMSN tion composition [20–25]. In this study, SMSN-incorporated poly(butyl methacrylate-co-ethylene glycol dimethacrylate) Surface modification of pristine SMSN with silanization re- monolith was prepared with the mixture of RTILs and agent γ-MPS was carried out according to our previous report DESs. To obtain SMSN-incorporated with robust column [13]. Synthesis method can be seen in the Electronic structure, SMSN were modified with silanization reagent Supporting Material (ESM). Microchim Acta (2018) 185: 444 Page 3 of 10 444

Preparation of SMSN incorporated monolithic column where μ refers to EOF, t is dead time, V is operating voltage.

L0 (32 cm) and L (42 cm) are stationary-based length and total Prior to the preparation of monolithic capillary, the inner wall length of capillary monolithic column, respectively. of fused silica capillary was dealt with NaOH solution Column permeability was evaluated by eq. 2 [26]. −1 (1 mol L ) for 30 min and washed with deionized water to μ L0 neutral, respectively. The capillary was then treated by BEK ¼ ð2Þ pumping γ-MPS/acetic acid aqueous solution (4/96, v/v) V −1 (6 mmol L ) for 90 min. The derivatized capillary was then where BEK refers to electrokinetic permeability. washed with deionized water to neutral and dried with N2 before use. Solid phase microextraction (SPME) The DESs were prepared by mixing choline chloride and chromatographic analysis (ChCl) with different type of alcohols. After a 24 h pretreat- ment of vacuum drying at 60 °C, the mixture of ChCl and The SPME procedures included pre-conditioning, sample alcohols was heated and stirred in oil bath of 100 °C for 3 h. loading, washing as well as desorption. A syringe pump The DESs obtained were homogeneous and viscous (RSP04-B, RISTRON, Zhejiang, China, www.chinamot.com) colourless liquid. The DESs were placed in drier before use. was employed for the SPME procedure. The procedure in For the preparation of SMSN incorporated polymer mono- detail for SPME of PAHs and lake water was as follows. For lith (Table S1), various contents of modified SMSN were dis- pre-conditioning, 0.2 mL methanol was in-drafted into the persed in a mixture containing BMA (0.175 mmol, functional syringe and injected through the SMSN incorporated mono- monomers), EDMA (0.075 mmol, cross-linking monomers) lith at 0.05 mL min−1, and then 0.5 mL phosphate solution and binary porogen, RTIL (65%, v/v) and DES (35%, v/v). (100 mM, pH 4.5) was injected at a flow rate of AMPS (1%, wt/wt%) and AIBN (1%, wt/wt%) were also 0.10 mL min−1. Likewise, 1.0 mL sample solution was intro- contained in the pre-polymerization mixture as electroosmotic duced into the syringe and passed though the monolith at flow provider and initiator, respectively. After vortexed and 0.10 mL min−1. After that, 0.2 mL phosphate solution sonicated, the homogenous pre-polymerization mixture was (100 mM, pH 4.5) was introduced into the monolith at a flow then filled into the derived capillary. Both outlet and inlet rate of 0.10 mL min−1. Subsequently, 0.1 mL mixture of meth- was sealed using rubber stopper. In situ polymerization was anol and H O(80/20,v/v) was injected into the monolith at carried out in water bath of 65 °C for 30 min. After reaction, 2 0.05 mL min−1 and the eluate was collected into a vial for the the resulting capillary column was washed with acetonitrile subsequent HPLC determinations. The SPME procedure of (ACN) to remove unreacted reagents. A detection window of quinolones (QNs) was performed according to previous report 2–3 mm length was burned at distance of 10 cm from the [27]. outlet. The corresponding monolith without SMSN was made The SPME device was fabricated according to Li’sgroup with same process in absence of modified SMSN. [28]. HPLC analysis was performed on an Agilent 1260 liquid chromatography system, equipped with a multiple wavelength Electrochromatography detector, and a quaternary pump and degasser. ChemStation software was applied for instrumental controlling and data – CEC was conducted using Kaiao K1050 high performance analysis. A reverse phase 100 5-C18 column (4.6 × 250 mm, capillary electrophoresis instrument (Beijing, China) Kromasil, Sweden) was employed for the chromatographic equipped with ultraviolet detector. Detection wavelength of analysis. Before analysis, a series of PAHs and QNs standard 254 nm was used and separation was performed at an operat- solutions and the lake water were filtered with a membrane μ ing voltage of 15 kV. Chromatographic workstation, CXTH- filter of 0.22 m. 3000, was applied for instrumental controlling and data analysis. Before CEC analysis, all capillaries were rinsed with mobile phase, which was filtered through 0.2 μmmembrane Results and discussion before experiment. The mobile phase was a various ratio mixture of acetonitrile and acetate buffer, consisted of the solution Characterization of the SMSN-loaded monolith of acetic acid and sodium acetate with different proportion and concentration. Particle size distribution of the SMSN is showed in Fig. 1. Electroosmotic flow (EOF) was evaluated by eq. (1)[26]: Over 90% of SMSN had a particle size of about 90 nm. L L Furthermore, the morphology of the SMSN incorporated μ ¼ 0 ð Þ tV 1 monoliths was tested by field emission scanning electron microscopy (FESEM). Compared with the SMSN-free monolith, 444 Page 4 of 10 Microchim Acta (2018) 185: 444

specific surface area of the SMSN incorporated monolith is increased about 28.18% by comparing the surface area of the incorporated (41.892 m2 g−1)andfreemono- lith (32.683 m2 g−1). Both the incorporated monolith and free monolithic column demonstrated incomplete isotherms of type II and hysteresis loops of type H3 [29]. Distinction of pore structure between the monolithic columns was observed. As a whole, the incorporation of SMSN with polymer matrix affects the resulting hybrid monolithic column system positively and significantly.

Optimization of polymerization variables Fig. 1 The size distribution of stellated mesoporous silica nanoparticles (SMSN) In order to obtain the best monolith, the influence of preparation variables was systematically studied. The fol- the microstructure in the SMSN incorporated capillary mono- lowing parameters were optimized: (a) SMSN content; (b) lith is denser with lower interstitial porosity (Fig. 2). As shown crosslinking monomer content; (c) type of RTILs cation in Fig. 3, the successful incorporation of SMSN into polymer and anion; (d) type of DESs; (e) percentage of DESs in matrix is further demonstrated by transmission electron mi- binary porogens. Respective data and figures are given in croscopy (TEM). Moreover, area scanning of energy dis- the ESM. The following experimental conditions were persive spectrometer (EDS) is employed to confirm a ho- found to give the best results: (a) SMSN content: 7.5% mogeneous distribution of SMSN in the resulting monolith (wt/wt%); (b) crosslinking monomer content: 30%; (c)

(Fig. S1). type of RTILs cation and anion: [HMIM]BF4; (d) type Pore property of both the incorporated monolith and of DESs: ChCl-PG (1, 2-propylene glycol); (e) percentage the free monolith were studied by N2 adsorption exper- of DESs in binary porogens: 35% (v/v). The resulting iments. The isotherms of nitrogen adsorption-desorption capillary monolith demonstrated uniform structure with for the SMSN incorporated and SMSN-free monolith good column permeability. Baseline separation of all are exhibited in Fig. S2. The Brunauer-Emmett-Teller analytes measured was obtained.

Fig. 2 The image of field emission scanning electron microscopy of SMSN incorporated monolith (a, c), SMSN-free monolith (b, d) Microchim Acta (2018) 185: 444 Page 5 of 10 444

For alkylbenzene samples containing eight compounds, baseline separation and high column efficiency (266,000 plates m−1) are obtained in less than 15 min on the SMSN incorporated monolith (Fig. 4a). Elution order was as follow: acetone, 2, 5-dihydroxyacetophenone, acetophenone, butyrophenone, toluene, ethylbenzene, propylbenzene, butylbenzene. On the contrary, the SMSN-free monolith exhibited unsatisfied separation performance with unsymmetri- cal peak shape and baseline separation was not realized in the same experimental conditions. The stronger retention on the SMSN incorporated monolith is due to the introduction of silanized SMSN onto the polymer matrix. Naphthalenes were used as analytes to study the potential of SMSN incorporated monolith in separation enhancement of π-electron rich compounds. With increasing elution time of 1-bromonaphthalene >1-chloronaphthalene >1- methylnaphthalene >1-naphthol, baseline separation is achieved (Fig. 4b). Compared with the SMSN-free monolith, the increasing resolution on the SMSN incorporated monolith can be due to successful combination of marcopores from polymer matrix with mesopores from SMSN. To further display the versatility of the SMSN incorporated monolith, alkaline analytes, and anilines were also separated in CEC mode. The retention time increased with an order of 1- naphthylamine >2-nitroaniline >4-fluoroaniline > acetanilide (Fig. 4c). All the analytes are baseline separated in ten minutes

(Rs > 1.5). In contrast, the SMSN-free monolith failed to sep- arate 4-fluoroaniline and 2-nitroaniline. Practically, the hybrid capillary fabricated with SMSN enhances separation for aniline compounds. In contrast to the unsuccessful separation on the SMSN-free monolith, three phenols were separated per- fectly on the SMSN incorporated monolith. The elution time of phenols is in an order of resorcinol < m-cresol <2, 6-dichlorophenol, indicating that hydrophobicity acts as a main role during phenols elution (Fig. 4d). Hydrophobic interaction between stationary phase and Fig. 3 Transmission electron micrographs of SMSN-incorporated analytes increases as the hydrophobicity of phenols in- a b c monolith ( ), SMSN-free monolith ( )andSMSNs( ) creasing, which leads to the successful separation of phenols analytes. For the purpose of investigating applicability, polycyclic Electrochromatographic evaluation aromatic hydrocarbons (PAHs), nonsteroidal antiinflammatory drugs (NSAIDs) and hydroxybenzoic acid To investigate the performance of the formed SMSN incorpo- (HBA) isomers were separated on the SMSN incorporated rated monolith and corresponding neat SMSN-free monolith, monolith. Baseline separation of PAHs, NSAIDs and HBA the separation for small molecules was performed by CEC. isomers is observed on SMSN incorporated monolith (C1) Four groups of small molecules were chosen as model com- in CEC mode (Fig. 5). The result indicates that the SMSN pounds, including alkylbenzenes, anilines, naphthalenes and incorporated monolithic column possesses adequate separa- phenols. The SMSN incorporated monolith exhibited im- tion ability for PAHs, NSAIDSs and HBA isomers. proved performance in terms of resolution and column effi- Quinolones (QNs) were also chosen to investigate the separa- ciency for the model compounds above compared to the tion selectivity of the SMSN incorporated monolith stationary SMSN-free monolith (Fig. 4). phase (Fig. S3). However, QNs cannot be separated on the 444 Page 6 of 10 Microchim Acta (2018) 185: 444

Fig. 4 Comparison of incorporated monolith and free monolith on acetonitrile/acetate buffer (pH 6.0, a mixture of acetic acid and sodium separation. Conditions: capillary, 100 μm inner diameter, 42 cm total acetate solution) (70/30, v/v). Analytes: a alkylbenzenes; b anilines; c length and 32 cm effective length; separation voltage, 15 kV; naphthalenes; d phenols temperature, 25 °C; UV-vis detector, 254 nm. Mobile phase:

resulting monolith. The result indicates that the resulting The major limitation of this method is a need of the accu- monolith has selectivity for the substances containing carbox- rate control of polymerization temperature and time during the yl group. preparation. No change of the temperature (65 °C) and time A number of monoliths with incorporation of meso- (30 min) had to be used. Otherwise, other polymerization porous silica nanoparticles to monoliths have been re- temperature or time would result in block monolith. Thus, ported [15, 30–32]. Table 1 compares the analytes for the variation in the polymerization temperature and time can separation, column efficiency and other characteristic not be utilized as polymerization variables for the optimiza- features of our work with other reports. Although the tion of monolith preparation. column efficiency of our columns was lower than the result of Lei and Wan’sgroup[30, 31], the SMSN in- Extraction of PAHs and quinolones (QNs) corporated monolith showed a remarkable enhanced retention accompanied with a better batch-to-batch repeat- To evaluate further the performance of the incorporated mono- ability. Because repeatability of the hybrid monolithic lith, capillary C1 was selected for SPME to PAHs and QNs. column is mainly determined by the stability of the Increasing the quantity of polymer in volume may improve column with nanoparticles embedded, it seemed that the SPME extraction efficiency, and therefore the preparation the silylation modification of pristine SMSN played an conditions and extraction device were modified accordingly: important role in the SMSN incorporated monolith. (1) the ID of capillary to prepare SMSN incorporated mono- Moreover, much more types of analytes can be separat- lith was enlarged to 250 μm; (2) the length of the incorporated ed on the SMSN incorporated monolith than other monolith was shortened to 20 cm to speed up the procedure; mesoporous silica nanoparticles incorporated monoliths. (3) the time of polymerization was prolonged to 1 h. The Microchim Acta (2018) 185: 444 Page 7 of 10 444 work 30 ] 31 ] 15 ] 32 ] Ref. ) 1 − 69,000-140,000 [ 24,000-290,000 [ Efficiency (plates m 118,000-266,000 Present 90,000-280,000 [ 157,000-209,000 [ enzoic acid derivatives ugs, and hydroxybenzoic acid isomers. enzoic acid derivatives nonsteroidal antiinflammatory dr Benzoic acid derivatives Thiourea, o-xylene, naphthalene and b Phenol series, naphthyl substitutes, aniline series, alkyl benzenes, polycyclic aromatic hydrocarbons,

Fig. 5 a Application of incorporated monolith and free monolith on PAHs separation. Conditions were same as Fig. 4. b Application of ous silica stationary phases for the separation of small molecules SMSN incorporated monolith and SMSN-free monolith on NSAIDs sep-

c 41 or UVM-7 Alkyl benzenes, cresols and b aration. Conditions were same as Fig. 4. Application of incorporated 15 monolith and free monolith on HBA isomers separation. Conditions: UV- vis detector, 210 nm. Mobile phase: acetonitrile/0.01 mol L−1 sodium ) and poly hydrogen phosphate (pH 10.0) (20/80, v/v). Other conditions were same 2

as Fig. 4 /NH 2 ) monolithic columns 2 @SiO 4 O washing liquid and the eluate after the SPME were collected 3 for HPLC analysis. Four PAHs (anthracene, fluoranthene, phenanthrene and fluorene) and four QNs (ciprofloxacin, norfloxacin, enrofloxacin and gatifloxacin) were selected as An overview on recently reported mesopor model analytes to study the potential in extraction and enrichment. The concentration of each component in the mixed −1 (BMA-EDMA-SBA-15/NH Table 1 Hybrid monolithic TEOS-APTES-with SBA- Poly(BMA-EDMA) with incorporated MCM- MCM-41-MPS incorporated monoliths Phenol series, naphthyl substitutes, aniline series and alkyl benzenes Poly(BMA-EDMA-Fe Material Analytes standard sample was 0.1 μgmL . HPLC chromatograms Poly(BMA-EDMA) with incorporated SMSNs 444 Page 8 of 10 Microchim Acta (2018) 185: 444 are shown in Fig. S4. Peak area of each analyte before and after SPME was used to determine the extraction efficiency of the resulting capillary monolith (Table 2).Therecoveryofthe analytes was all above 80%, showing that the SMSN incorporated monolith is a reliable SPME material for extraction of PAHs and QNs. Moreover, compared with QNs, the resulting capillary monolith is more suitable for extraction of PAHs.

Extraction of fluoranthene in lake water by SPME

The incorporated monolith was used to determine the trace fluoranthene, a common environmental pollution, in lake water. HPLC chromatograms of fluoranthene in the lake water after SPME are shown in Fig. 6a. The result indicates that the lake water contains only tiny amounts of fluoranthene. The recovery of fluoranthene of the lake water after SPME was 93.43%. As shown in Fig. 6b, the SMSN incorporation into monolithic column can significantly improve extraction efficiency and the hybrid monolith exhibits greater separation ability for complex samples. In our study, the concentration ranging from 0.2 to 1.8 μgmL−1 of standard fluoranthene solutions was chosen to validate the method for the quantification and the linearity. There was a good linear relationship with R2 of 0.9994, the limit of detection (LOD, 3 times the standard deviation of the Fig. 6 a Application of incorporated monolith on extraction of baseline noise) was 0.01 μgmL−1 and limit of quantitation fluoranthene in the lake water. b Comparison of incorporated monolith (LOQ, 10 times the standard deviation of the baseline noise) and free monolith on SPME. Conditions: UV-vis detector, 250 nm. Mobile phase: methanol/H O (85/15, v/v), flow rate: 1.0 mL min−1 was 0.04 μgmL−1. The relative standard deviations (RSDs), 2 the intra-capillary and inter-capillary reproducibility of the injections in CEC mode, and no obvious damage of the struc- method were all less than 3.0% (three replicate experiments). ture of the monolith was found. The reproducibility of the These results suggested that the application of the resulting monolithic column fabricated with C1 was evaluated by in- SMSN incorporated monolithic column for SPME is reliable. vestigating the migration times, selectivity factor and retention factor of alkylbenzenes in a series of injections (Table S2). Reproducibility of SMSN incorporated monolithic The RSDs of retention times and selectivity factor for batch- column to-batch and run-to-run of the incorporated monolith were all less than 0.6%. The RSDs of retention parameters for batch- The resulting incorporated monolith can afford baseline sep- to-batch and run-to-run of the SMSN incorporated monolithic aration to the analytes after more than one hundred times of column were less than 2.0% (n = 3) and 1.0% (n =5), respectively. Table 2 Peak area and recovery of each analyte before and after SPME

Analyte Peak Area (mAU ∙ min) Recovery (%) Conclusion Standard sample Eluting sample

Fluorene 15.6640 156.3305 99.80 In this work, a novel SMSN incorporated monolith was suc- Phenanthrene 34.3840 340.4787 99.02 cessfully prepared and used as stationary phase for CEC and Anthracene 70.8673 696.2918 98.25 solid phase microextraction. The binary porogens, Fuoranthene 10.9156 101.8384 93.30 [HMIM]BF4 and ChCl-PG, exhibited excellent dispersible Ciprofloxacin 17.8162 147.8930 83.01 property for SMSN and can lead to hybrid monolithic column Norfloxacin 17.2440 146.6110 85.02 with good column permeability. The formed hybrid monolith Enrofloxacin 33.5391 295.1659 88.01 incorporated SMSN demonstrated improved chromatographic Gatifloxacin 38.8507 329.2542 84.75 performance for small organic molecules, including alkylbenzenes, anilines, naphthalenes and phenols. The Microchim Acta (2018) 185: 444 Page 9 of 10 444 highest column efficiency achieved was 266,000 plates m−1 liquid chromatographic separation of small molecules. Chem – for alkylbenzenes analysis. 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